Weight saving and manufacturing cost benefits have led to the increase in use of organic matrix fiber reinforced composite structures in the aircraft and aerospace industries. In order to be a viable alternative to metal these composites should maintain the strength typical of conventional structural systems. In many applications composites are put under a variety of environmental and mechanical stresses. For example, frequently these composites are exposed over long periods of time to elevated temperatures which can result in a loss of composite properties. The loss of properties can result from heat induced microcracks that allow oxygen to attack the fibers. As a result of this deficiency, extensive research and development efforts have been undertaken to define methods and identify materials which improve composite performance in elevated temperatures. For example, it is known that surface preparation of fibers can be important in the formation of composites. Thus, the fiber can be coated with an organic primer or sizing agent to produce a surface which when combined with the matrix resin develops the strengths which meet application requirements. A variety of sizing agents have been used to produce improved bondability including epoxy, polyimide and polyvinylacetate polymers. In particular, commonly assigned U.S. Pat. No. 4,678,820 describes an amorphous hydrated metal oxide primer as a fiber size that provides improved wet strength to a fabricated composite. Although the above surface preparations have provided advantages, there is a need for new technology to aid in the advancement of lightweight aerospace-type composite structures.
Accordingly, there is a constant search in this field of art for new methods of providing lightweight, structurally sound composites.